Process for preparing poly(alpha, alpha-disubstituted beta-lactams)



United States Patent 1 Claim. (Cl. 260-78) This is a division of myapplication Ser. No. 271,598, filed Apr. 9, 1963, now U.S. Patent3,297,754.

This invention relates to anovel process for preparing polyamides froma,a-disubstituted-B-halopropionic acid amides by way of p-lactams.

B-Lactams, which are the inner cyclic amides of amino acids, are notnormally made directly from the amino acid. The parent compound of theB-lactam series, p-propiolactam, is made by the action of a Grignardreagent upon fl-aminopropionic esters. B-Lactams bearing a hydrogen atomon the nitrogen, but having hydrocarbon groups on the u or ,B-carbonatoms, are also made by the same Grignard method, or by action of baseupon ,B-aminopropionic acid chlorides, or from olefins by a process asdescribed in German Patent 1,086,234. These methods are not desirableroutes to fl-lactams, particularly those having two substituents on thea-carbon atom, because of the costly raw materials or uneconomic yields.

This invention is concerned with polymers derived from u,a-disubstitutedB-amino acid units and with methods for preparing said polymers. Suchpolymers are particularly stable to hydrolytic, thermal, and photodegradation because attack on the amide linkage is hindered stericallyand because the NH group is neopentyl and is not subject toB-elimination reactions.

Polyamides comprising units of B-amino acids having two a-substituentshave a desirable combination of properties that renders them attractivefor commercial production of fibers for apparel and other uses. Selectedmembers of these polyamides have melting points less than 300 C. whichare sufficiently low to permit meltspinning into fibers, but at the sametime high enough to permit normal apparel usage. These selected membersare those polymers in which the a-substituents are alkyl. The highermelting members, those melting above 300 C., can be fabricated bysolution-spinning from, for example, methanolic calcium thiocyanate,formic acid, m-cresol, sulfuric acid, trifiuoro acetic acid, andchloroform.

It is an object of this invention to provide a new route to polyamideshaving two substituents on the acarbon atom. Another object is toprepare a high melting form of poly(pivalamide) which is melt-spinnableand is characterized by being soluble in chloroform.

Another object is to provide a new and convenient synthesis of,B-lactams having two alkyl groups on the a-carbon atom uncontaminatedwith [3,;3-disubstituted isomers.

A further object is to provide a rapid, high yield synthesis of highmolecular weight, fiber-forming polyamides from B-halopropionic acidshaving two substituents on the a-carbon atom.

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Another object is to prepare the N-alkali or alkaline earth metal saltsof a,a-disubstituted-fl-halopropionamides.

This invention provides a process for preparing fiberforming highmolecular Weight linear polyamides comprising units of ,B-amino acidshaving two hydrocarbons or monochloromethyl groups on the a-carbon atomsonly, without any flit-isomer, from a,a-disubstituted-[3- halopropionicacid amides. The process may be accomplished by reaction of selectedalkali or alkaline earth metal salts of weakly acidic compounds with thehaloamide in certain polar organic solvents and at elevated temperaturesto form the fi-lactam, and then polymerizing said lactarn in thepresence of a catalyst in selected polar organic solvents free of activehydrogen to form the polyamide. Alternatively, the haloamide may beconverted to the N-alkali metal salt or N-alkaline earth metal salt byreaction with the alkali or alkaline earth metal salt in a liquiddiluent. The N-metal salt of the haloamide may be cyclized by heat incertain polar solvents with elimination of metal halide to form the B-lactam which may be polymerized as before. In a preferred embodiment,the a-carbon is fully substituted by two monovalent alkyl groups or onedivalent polymethyl ene group.

These novel alkali or alkaline earth metal salts and the polyamidesformed by the process of this invention are produced by the followingreactions:

an a, a-disubstituted metal salt of the fl-haloamide an a,a-disubstituted B-lactam a polyamide In the above formulas, M representsan alkali or alkaline earth metal, preferably lithium, sodium, potassiumor calcium; X represents a halogen, preferably chlorine or bromine; Rrepresents hydrogen, a tertiary alkoxy group of no greater than sixcarbon atoms such as t-butoxy, or hydrocarbon of up to twenty carbonatoms; R and R which may be different represent monochloromethyl,phenyl, alkyl or cycloalkyl radicals of no more than six carbon atomseach, and may together form an alicyclic hydrocarbon ring incorporatingthe wcarbon atom; n is equal to the valence of M, i.e., 1 or 2, and m isa whole number suificiently large that the polyamide is fiber forming.

A coupled process which is of particular value for the formation of thepolyamides and in which the metal salt of the amide is not isolated, isaccomplished by the use of selected polar organic solvents free ofactive hydrogen as the reaction media. Usefulsolvents for this purposeare liquid under the reaction conditions and dissolve the amide, theN-alkali metal salt of the amide, and the lactam, and have at least aswelling action on the polyamide, but do not otherwise react with thesolutes; the solvents may or may not also dissolve the alkali halide(MX) formed in the first reaction. The preferred solvents are thosedistillable cyclic lactams which have a lower alkyl group on thenitrogen atom, such as N-methyl pyrrolidone and N-methyl caprolactam andlinear amides of the type RiCO-NR R where R =lower alkyl having 1, 2, 3carbon atoms and R and R =lower alkyl having 1, 2, or 3 carbon atoms ora ring composed of these units and the nitrogen, and boiling within therange 165- 400 C.

The B-halo amides used as the starting materials for the process of thisinvention may be prepared from 5- halo acids by the well-known sequenceof converting the acid to the acid chloride with thionyl chloride or aphosphorus chloride, followed by reaction of the resulting acid chloridewith aqueous ammonia, in a manner similar to that described in OrganicSyntheses, Collective Volume III, pages 490492 for the preparation ofisobutyramide. Halopivalamides may be made from monochloro trimethylacetonitrile, whose preparation from trimethyl acetonitrile is describedin British Patent 608,806, followed by conversion of the nitrile groupto an amide group using hydrogen peroxide according to the generalprocedure described in Organic Syntheses, Collective Volume II, page586. The 0:,oc-diSllbStitUt6d-[3- halopropionic acids may be made by thegeneral procedure disclosed in French Patent 1,231,163 from B-hydroxyaldehydes obtained by condensation of formaldehyde or other aldehydeswith oc,ot-diSl1bStitllt6d acetaldehydes (e.g., isobutyraldehyde). Thesefi-halo acids may also be made by the action of a hydrogen halide uponthe ,5- hydroxy acids obtained by saponification of the ester formed inthe self-condensation of ,B-hydroxy aldehydes. A self-condensation ofthis type has been described by Finch in the Journal of OrganicChemistry, vol. 25, page 121219 (1960) for u,a-dimethyl-fl-hydroxypropionaldeyde.

The alkali or alkaline earth metal derivatives used for preparing thelactams or the ,B-haloamide salts are the salts of replaceable hydrogencompounds having acid strengths lower than or equal to tertiary-butanol.They are prepared, for example, by reacting a tertiatry alcohol with analkali metal, and include substances such as potassium tertiarybutoxideand the sodium salt of Z-methyl- Z-butanol or metal derivatives ofweakly acidic compounds such as sodium hydride, sodium triphenylmethane,

and sodium naphthalene. The alkoxides employed are those derived fromtertiary alcohols Which boil at least 0., preferably at least 40 0.,below the lactam, to facilitate separation therefrom prior to thepolymerization. Equivalent amounts of alkali or alkaline earth metalderivatives and fi-halopropionic acid amide are normally employed.Sodium methoxide and similar salts of primary alcohols are not suitablereagents for effecting closure of the lactam ring, simple displacementof the [3- halogen by n-alkoxy taking place in preference todehydrohalogenation to lactam.

Polymerization of the lactams is eifected with a strongly basicpolymerization catalyst, such as for example, sodium hydride andoptionally may include an acyl promoter such as acetic anhydride. Otherillustrative catalysts are alkali lactamates, alkali tertiary-alkoxides,and alkali aryls and alkyls. They may be present in amounts of be tweenbout 0.001 and 0.02 mole per mole of lactam. Other acyl promoters areacetyl chloride, cyanuric chloride, and oxalyl chloride and are normallyemployed in amounts of between 5X10 and l 10- mole based on the lactam.

That the N-alkali or alkaline earth metal salts of thefl-halopropionamides are indeed intermediates in the preparation of thepropiolactams of this invention can be demonstrated by the isolation ofsuch salts and conversion of these to lactams by heating in a water-freeinert medium at temperatures of 60 to 140 C. The lactam may be isolatedby removal of the solvent followed by distillation. In one embodiment ofthis invention the N-alkali or alkaline earth metal salts are isolableby reaction of the B-haloproprionamide with sodium hydride at roomtemperature in a solvent of low polarity such as benzene, the N-alkalimetal salt being isolated by filtration and characterized by elementalanalysis. Subsequent heating alone or in the presence of a solvent whichdoes not con tain a reactive hydrogen converts the salt to lactam andmetal halide. The lactam may be polymerized by any of the processessubsequently described.

Preparation of the p-lactams from the fi-haloamides Without separationof any intermediate metal salt may be carried out at temperatures in therange of 20-l50 0, preferably at 70-120 C. The p-lactam and any activehydrogen containing solvent which is present are then codistilled asrapidly as the lactam is formed in order to avoid polymerization of thelactam in this medium. The reaction can be run under vacuum so that thelactam distills out as rapidly as it is formed, absolute pressures of0.1-20 mm. mercury being used. The temperature of the reaction mixtureis maintained at 20-100" C. above the boiling point of the lactamproduct at the pressure being used. For the preparation ofa,u-dimethyl-5-propiolactam, the reaction mixture is suitably maintainedat -110 C. at 5-10 mm. mercury absolute pressure.

One important aspect of the present invention is the use of certainpolar solvents in the formation of ,B-lactams from thea,a-disubstituted-B-halopropionic acid amide. Such polar solvents havedipole moments in excess of 1.55 Debye units when measured at or below20 C. and are those selected from the group consisting ofN,N-disubstituted amides, ethers, N-alkyl cyclic lactams, tertiaryalcohols, and dialkyl sulfoxides. The use of non-polar solvents such asbenzene or toluene in this step of the process gives rise to an impuritywhich is fi-hydroxy-a,adisubstituted propionitrile, which, unlessremoved prevents attainment of high molecular weight polymer. In thecase of pivalolactam preparation in non-polar solvents, the impurity ishydroxypivalonitrile. Surprisingly, none of this impurity is formed whenthe solvents are the more polar tetrahydrofuran or dimethyl acetamide.In the event some small amount of impurity is formed, it is soinsignificant that it does not interfere with the polymerizat1on processand therefore need not be removed. This is of importance sinceseparation and removal of the undesired nitrile is diflicult and costlyas exemplified in some of the examples which follow.

In carrying out the ring-closure step, haloamide is first dissolved orsuspended in the selected polar organic solvents described, in a vesselequipped with means for stirring. The mixture is then brought to thedesired operating temperature and pressure. A separate solution of thealkoxide in the same organic solvent or slurry of metal hydride or metalalkane is gradually run into the stirred amide solution. The lactamproduced distills out substantially as rapidly as it forms along with aportion of the solvent. The lactam may then be isolated from thedistillate mixture by fractional distillation. In order to facilitateremoval of the lactam as rapidly as it is formed, and to permit facileseparation of the lactam from the polar solvent by fractionaldistillation when so desired, it is preferable to use a solvent having aboiling point at least 20 different from that of the lactam, atpressures suitable for their separation. By carrying out thelactamforming reaction under conditions such that the solvent alsovaporizes, the purging action of the vaporizing solvent facilitatesremoval of the lactam as quickly as it is generated.

Polymerization of the lactam is carried out with a solution thereof in apolar organic solvent not possessing a labile hydrogen atom. Thequantity of solvent employedin this step as well as in theaforementioned operations is not critical. A sufficient amount ofsolvent (preferably from 1 to 15 vol. of solvent per vol. of ,6-lactam)to achieve solution of the reactants and product and thus provide asuitable reaction medium is normally employed. The presence of excessiveamounts of solvent are uneconomical since costly removal is thenrequired and the molecular weight of the obtained polymer is lower.

The solution is maintained at a temperature in the range of 20-90 0.,preferably 40-70 C., for a period of 0.2 to hours to effect thepolymerization. Formation of the polymer converts the solution to agel-like mass. The polymer is isolated from the polymerization medium bymixing with a liquid such as water, which is a non-solvent for thepolymer, but which is miscible with the solvent. The resulting crumblikepolymer par ticles are readily filtered and washed, giving asubstantially quantitative yield of polymer that is suitable forconversion to shaped structures, such as fibers, without fuitherpurification.

In one further embodiment of this invention, wherein the alkali oralkaline earth metal salt of the haloarnide is converted to the lactam,the formation of the lactam and its polymerization may be carried out inthe same solvent without intermediate isolation of the salt or thelactam from the solvent. The lactam solution distillate that is obtainedfrom the first step is purified by fractional distillation to removeimpurities such as any tertiary alcohol by-product formed in the ringclosure. It is generally sufiicient to merely distill out theby-products from the lactam solution, the latter then being suificientlypure for direct preparation of high-quality polyamide. The catalyst andpromoter are merely added to the solution at the dedescribed by Backetet al. in Recueil des travaux chimiques mation of the polyamide iscomplete.

Although a variety of polar organic solvents free of active hydrogen maybe used in the polymerization step of this invention, N-lower-alkylderivatives of lactams having 4 to 7 members in the ring are preferred.Lactams of this type include N-methyl azetidinone-2,N-methylpyrrolidone-Z, N-ethyl-pyrrolidone 2, N-butyl-pyrrolidone 2,N-methyl-piperidone 2, N-ethyl-piperidone-Z, N-propyl-pyrrolidone 2, Nmethyl-w-caprolactam, N- ethyl w caprolactam, N-propyl w caprolactam,and the like. Other polar organic solvents that may be used includedimethyl sulfoxide, hexamethylphosphoramide, and dimethylacetamide. Theuse of relatively non-polar solvents such as benzene, petroleum ether,cyclohexane, etc., or no solvent at all, gives only low molecular Weightpolyamide in the polymerization step.

The a,a-disubstituted-fi-halo propionic acid amides which may beconverted to the alkali metal salts of the haloamides and topolymerizable lactams according to this invention include those derivedfrom u,a-dimethylfi-halopropionic acids (also known as halo-pivalicacids), a,u-diethyl-fl-halopropionic acids, 01,04dipropyl-fl-halopropionic acids, a,a-dibutyl ,8 halopropionic acids;mixed dialkyl acids such as a methyl-a-ethyl-fl-halopropionic acids;cycloalkanes bearing both a carboxylic acid group and a halomethyl groupon the same carbon atom, such as 1 halomethylcyclobutanecarboxylicacids, 1 halomethylcyclopentanecarboxylic acids, 1halomethylcyclohexanecarboxylic acids, 1halornethylcycloheptanecarboxylic acids, and lhalomethylcyclooctanecarboxylic acids; or,a-diphenyl-B-halopropionicacids, ot,0tdi-p-tolyl-fl-halopropionic acids; andu-alkyl-ot-aryl-fl-halopropionic acids wherein the alkyl and aryl groupsare those disclosed herein.

The above process is of particular value in converting thea,a-disubstituted lactam to its polymer exclusive of the [Mi-isomer. Thepolymer made from u,a-dimethyl lactam is found to be highly crystalline,soluble in chloroform, and has a crystalline melting point of not lessthan 260 C. and in most instances melts at 273-274 C. as determined byX-ray hot camera method and by differential thermal analytical methods.

Although not intended to limit the scope thereof in any way, thefollowing examples serve to illustrate this invention.

EXAMPLE I Bromopivalic acid, which is prepared by the proceduredescribed by Backer et al. in Recueil des travaus chimiques desPays-Bas, vol. 55, page 897 (1936) is refluxed with thionyl chloride toform bromopivaloyl chloride. The latter is isolated from the reaction byfractional distillation and subsequently converted to t? bromopivalamidethrough the action of aqueous ammonia, in a manner similar to thatdescribed in Organic Syntheses, Collective Volume III, pages 490-492,for the preparation of isobutyramide from isobutyric acid, The B-haloamides employed in the remaining examples are prepared from therespective ,B-halo acids, by the same reaction sequence unless otherwisenoted.

A solution of 36 grams (0.20 mole) of B-bromopivalamide and 22.6 grams(0.20 mole) of potassium tertiary-butoxide in ml. ofN-methylcaprolactarn is heated in a dry nitrogen atmosphere at 100 C.for 45 minutes. The tertiary butanol formed is removed by vacuumdistillation and the residual product, 3,3 dimethyl azetidinone-Z, andthe solvent are thencodistilled in vacuo at 100-110 C./ 13 mm. Thedistillate is separated into the two components by gas chromatography orby fractional distillation in an effective distillation column to yield17 grams (0.017 mole) of the pivalolactam.

EXAMPLE II The Example I procedure is utilized in effecting a reactionbetween 28.0 grams of fi-chloropivalamide (0.20 mole), which is preparedfrom chloropivalic acid made according to US. Patent 2,302,228 and 22.6grams of potassium tertiary-butoxide (0.20 mole) in 100 m1. of N-methylcaprolactam. This solution is heated in a dry nitrogen atmosphereat C. for 2 hours at atmospheric pressure. Separation of the componentscontained in the reaction vessel by the procedures of Example I yields amajor portion of N-methylcaprolactam and 13 grams of pivalolactam (0.13mole), n 1.449.

EXAMPLE III 75.8 grams (0.36 mole) of a,a-diethyl-p-bromopropionamide,which is prepared from a, x-diethyl 13 bromopropionic acid made by themethod disclosed in French Patent 1,231,163, are refluxed in a nitrogenatmosphere with 40.8 grams (0.36 mole) of potassium tertiary-bu toxidein 500 ml. of tertiary-butanol for 45 minutes. The solution is filteredand the clear filtrate is distilled to separate the major portion of thetertiary butanol from the lactam. The lactam-rich residue is thenfractionated to yield 41 grams (0.32 mole) of 3,3-diethylazetidinone-2,B.P. 79-82 C./0.5 mm., n 1.461.

EXAMPLE IV The influence of the kind of solvent and basic reagent uponthe ring-closure of s-haloamides to fi-lactams is shown in a series ofexperiments utilizing a variety of said solvents and reagents.

The general procedure shown in Examples I and II is used in carrying outthis series of experiments, in which either fl-chloropivalamide (Items16-19) or ,B-bromopivalamide, (Items 1-15) is converted to pivalolactam.The main features of these experiments are summarized in the followingtable.

TAB LE L-PIVALO LACTAM FROM HALO PIVALAMIDES Amount Amount Amount TimeTemp. Weight Percent Item Amide Basic Reagent Basic Solvent Solvent(min) C.) Lactam Yield (g.) Reagent (ml) (g.)

20 120 100 0. 6 18. 1 81 3. 7 37 36. 2 720 81 10. 3 52 36. 2 240 111 9.7 49 18. 1 720 135 18. 1 720 81 36. 2 240 102 8. 6 43 18. 1 420 156 18.1 60 150 18. 1 Tribenzyl Amine 180 180 36.0 Potassium tert.-butoxide 15083 16.1 3 86 36. 2 NaI-I 300 83 17. 8 90 36.0 Potassium tert.-butoxide45 100 17.0 86 36. 2 Potassium tert.-butoxide 180 81 13. 0 65. 5 18. 1Potassium tert.-butoxide. 100 6. 8 68 34 NaH (53.5% in Mineral Oil) 1112. 5 9 26. 9 Potassium tert.-butoxide 300 83 9. 4 3 60 75 Sodiumtert.-amylate 240 120 37 68 28 Potassium tert.-butoxide 120 120 13 66 147% in mineral oil. 2 No reaction. 3 Based on recovery of startingmaterial.

EXAMPLE V A reaction mixture composed of 20 grams (0.091 male of oc,ol.pentamethylene [3 bromopropionamide, which is prepared froma,a-pentamethylene-fi-bromopropicnic acid made by the proceduredescribed in French Patent 1,231,163, 10.7 grams (0.096 mole) ofpotassium tertiary-butoxide, and 500 ml. of dry tertiary-butanol isrefluxed for 1 hour under a nitrogen atmosphere. The potassiurn bromideformed during the reaction is removed by filtration and thetertiary-butanol is removed from the filtrate by distillation underreduced pressure. The residue, composed of the virtually purefi-lacta-m, is purified by recrystallization from benzene/heptane (1/5volume ratio) or by sublimation in vacuo at 70-75 C./ 0.2 mm. to yield11.3 grams (0.081 mole) of 3,3-pentamethylene-/3-propiolactam, MSP.73.5-75" C.

EXAMPLE VI To 22 grams (0:073 moles) ofu,u-diphenyl-,8-bromopropionamide which is made by the method describedby Zaugg et al. in the Journal of the American Chemical Society, vol.72, page 3006 (1950), dissolved in 100 ml. of tertiary-butanol, is added11.8 grams (0.11 mole) of anhydrous potassium tertiary butoxide. Themixture is stirred and refluxed in a nitrogen atmosphere at 85 C. for 45minutes. The milky white liquid is then filtered to remove the potassiumbromide formed and the tertiary-butanol is removed from the filtrate bydistillation under reduced pressure. The residue, a slightly yellowsolid, is recrystallized from benzene in the presence of an activecarbon decolorizer (Dar-co) to yield 10.6 grams (0.048 mole) of3,3-dipheny1azetidinone-2 as colorless crystals, MJP. 171 C. It is to benoted that use of an excess of potassium tertiary butoxide resulted in alower yield of ,8- iactam in comparison to those examples in which thering-closure reagent and the haloamide are present in equimolarquantities.

EXAMPLE VII A solution is prepared in an atmosphere of dry nitrogen from4 grams pivalacta-m, .025 grams sodium hydride, and 10 ml.N-methyl-pyrrolidone-2. This solution is then kept at 60 C., for 3.75hrs. The resulting gel-like mixture is then stirredwith water to convertthe poly- (pivalamide) that has been formed therein to a particulateform. After being removed by filtration, washed with water, and dried,the polyamide weighs 3.8 grams and has an inherent viscosity in m-cresolsolution (0.5%) of 0.70.

Abbreviations: NMO-N-methyl eaprolactam; DMAQ-Dimcthylacetamide;TMSOTetramethylene Sulfone; DMF-Drmcthylformamide;DMSO-Dimethylsulfoxide; NMP-N-methylpyrrolidone-2.

EXAMPLE VIII A solution is prepared in an atmosphere of dry nitrogenfrom 10 grams of 3,3-pentamethyleue azetidinone-2, 25 ml. of N-methylcaprolactam, and 250 mg. of a 47% sodium hydride suspension in parafiinoil. This solution is then kept at 65 C. for 4 hrs. The polymer,2,2,-pentamethylene-3-polyamide, is then precipitated by the addition of500 ml. of water. The polyamide, removed by filtration, washed withwater, and dried, weighs 9.1 grams. The polymer has a crystallinemelting point of 275 C. and an inherent viscosity in m-cresol solutionof 1.43.

EXAMPLE IX To a solution of 15 grams of pivalolactam in 120 grams offreshly distilled hexamethylphosphoramide is added mg. of sodium hydrideand, following the disappearance of the sodium hydride, 2 drops ofacetic anhydride. The solution is kept in a closed flask at 65 C. for 4hours, during which period the solution becomes very viscous. Thep0ly(pivalamide) is precipitated by the addition of water, removed byfiltration, washed with Water, and dried to a weight of 14.5 grams. Thepolymer has a crystalline melting point of 273 C. and an inherentviscosity in m-cresol (0.5%) of 2.12.

Table II, below, contains representative fiber data for fibers obtainedby press spinning poly(pivalamide) (inherent viscosity 2.1, 0.5% inm-cresol) at 280-288 C. and "by winding up the fiber at a speed of300-315 yd./ min. The fibers were extruded into a bath containingsilicone oil Dow 555, serving as a quench and as a protective coating.Finally the extruded fiber is drawn 1.1X at C.

TABLE II.FIBER DATA FOR POLY(PIVALAMIDE) Conditions (all samplesTenacity, Percent Initial boiled oft) grams/denier Elongation Modulus,

grams/denier 21 0., 65% R.H 3.3 40 73 1 C. 3. 1 45 7 2. 5 28 23 1. 7 345 These fibers are non-yellowing after a 700-hour lightstability testand display only a 44% drop in inherent viscosity after this lengthytesting. The light stability test is performed in an Atlas ColorFade-Ometer, Model FDA-- R, in which the carbon arc is replaced by axenon-filled lamp, type Osram XBF-6000, which is water cooled and has aminimum coolant flow of 6 liters per minute, an AC-current supplyvoltage of 220 volts, an operating voltage of 135 volts, an operatingamperage of 45 amperes, and a rated power of 6000 watts. The fibersamples are placed on 9'1-lb. Bristol Index cardboard strips which areplaced on the rotating framework of the Fade-Ometer at a distance of 10inches from the center of the lamp. The temperature surrounding thefiber samples is 145:5" F. In this modified device the fibers aresubjected to a lightstability test that is 2-3 times as severe as thatresulting from the use of the carbon are light source.

The hydrolytic stability of the polymer is excellent, and the polymerstands a 4-hour boiling test in 10% sodium hydroxide solution withoutany weight loss or loss in inherent viscosity.

EXAMPLE X To 27 grams of 3,3-diethylazetidinone-2 dissolved in 40 ml. ofhexamethylphosphoramide is added 100 mg. of sodium hydride and, when thelatter is dissolved, 2 drops of acetic anhydride. This solution is keptbetween 65-70 C. for 48 hours. The resulting viscous solution is thenagitated with water in an Osterizer-type blender to form a white,polymeric precipitate which, following isolation, washing, and drying,weighs 20.2 grams, possesses a melting point of 205 C., and has aninherent viscosity of 0.73.

The polymer can be press spun at 210 C. at a windup speed of 275ft./min. into fibers which on drawing 4.5X at '68-7 C. showed thephysical properties tabulated below in Table III.

TABLE IIL-FIBER DATA FOR POLY(A,A-DIETHY-B-AMINO- A solution of 40 ml.of N-methyl caprolactam containing 3.8 grams of pivalolacta-m issubjected to ring opening polymerization by the addition of 50 mg. ofsodium hydride (in a 47% suspension in mineral oil), with heating beingmaintained at 65 C. for 24 hours under :1 nitrogen atmosphere. Thepoly(pivalamide) thus obtained weighs 3.6 grams and has an inherentviscosity of 1.45.

EXAMPLE XII This example shows the preparation and polymerization ofpivalolactam in solution without intermediate separation therefrom.

A solution is prepared from 3. 6 grams of the amide of bromopivalic acidand 12 ml. of N-methylcaprolactam in a 50-ml. glass flask; 2.26 grams offinely powdered potassium tertiary-butoxide is then added to thatsolution. The resulting mixture becomes opaque and warm. The reaction iscompleted in the course of distilling the mixture to dryness at 90-110C./ 8 mm, the small amount of tertiary-butanol being separated byfractionation. The distillate remaining consists of about 13 ml. of acolorless liquid containing pivalolactam. Most of the distillationresidue is readily water-soluble; the material that does not dissolve is.35 gram of polypivalamide.

The lactam contained in the distillate is converted to a polyamide byadding .030 gram sodium hydride and maintaining the temperature at 50 C.for 2 hrs. under a nitrogen atmosphere. The poly(pivalamide) formedthere'- by is isolated from the viscous reaction product by stirringwith water; it weighs 1.45 grams after washing and drying, and melts atabout 260 C. This polyarnide is combined with the 0.35 gram quantityisolated from the distillation residue; the resulting mixture ispurified by dissolving in formic acid with the application of heat,filtering, and then re-precipitating by the addition of water.

10 The resulting polymer has an inherent viscosity of 0.64, measured inm-cresol solution at 0.5% concentration, and forms coherent films whencast from formic acid solution.

EXAMPLE XIII A solution of 30 grams (0.14mole) of oc,a-diet-hyl- 3-bromopropionamide in 150 ml. of N-methyl caprolactam is heated in vacuo(0.3 mm. Hg pressure) to the boiling point of the N-methyl caprolactam-A solution of 16.2 grams (0.14 mole) of potassium tertiary-butoxide in100 ml. of N-methyl caprolactam is then added, in 10-ml. portions, tothe amide solution and the N-methyl caprolactam is allowed to distillrapidly at -100 C. together with the 3,3-diethylazetidinone-2 that isformed. The tertiary-butanol is stripped from the distillate and the 3-lactam is then polymerized in the residual solution to yield 16.1 gramsof poly(a,a-diethyl-fi-aminopropionic acid).

EXAMPLE XI V All operations described below are carried out in a dryboxunder nitrogen at room temperature.

(a) Sodium: salt of chloropivalamide 13.55 grams (0.1 mole) ofchloropivalamide are dispersed in 200 ml. dry diethyl ether in anatmosphere of dry nitrogen and 4.75 grams (0.1 mole) of a 50.6% sodiumhydride dispersion in paraffin oil are added in small portions. Avigorous evolution of hydrogen results and from the initially nonviscoussolution, which is stirred magnetically, the sodium salt ofchloropivalamide precipitates in a period of two minutes. The salt isremoved by filtration and washed with dry ethyl ether and petroleumether. The yield is 13.0 grams (0.082 mole).

Analysis-Calculated for C H NOCINa: C, 38.1%; H, 5.8%; N, 8.6%. Found:C, 38.2%; H, 5.7%; N, 8.9%.

(b) Sodium salt of bromopivalamide The procedure of (a) was employed butwith the following reagents:

18.0 grams (0.1 mole) of bromopivalamide,

4.47 grams (0.1 mole) of a 50.6% sodium hydride dispersion in parafiinoil,

200 ml. dry ether. The yield is 17.6 grams (0.087 mole).

Analysis.Calculated for C H NOBrNa: N, 6.9%; Br, 39.5%. Found: N, 6.7%;Er, 39.4%.

(c) Potassium salt of bromopivalamiae The procedure of (a) was employedbut with the following reagents:

18.0 grams (0.1 mole) of bromopivalamide,

11.3 grams (0.1 mole) of potassium tertiary-butoxide in 400 ml. dryether. The yield is 6.8 grams (0.031 mole), the lower yield due to thehigher solubility of the potassium salt in ether.

Analysis.-Calculated for C H NOBrK: C, 27.5%; H, 4.2%; N, 6.2%. Found:C, 27.5%; H, 4.5%; N, 6.4%..

The potassium salt of chloropivalamide is obtained in an identicalprocedure from chloropivalamide and potassium tertiary-butoxide, as arethe alkali and alkaline earth metal salts of otherB-halo-a,u-disubstituted-propionamides wherein the a-positionsubstituents are hydrocarbon groups which may be the same or dilferent.

EXAMPLE XV A solution of 3.5 grams (0.018 mole) of the potassium salt ofbromopivalamide in 18 ml. of N-methylcaprolactam is heated at 90-100 C.for 25 minutes to produce 3,3- dimethylazetidinone-Z by ring closure.This product is codistilled in vacuo with the solvent at -110 C./l3 mm.Separation of the components by fractional distillation yields 1.7 grams(0.017 mole) of pivalolactam.

The process of this invention may not only be utilized in batch-type andsemi-continuous operation, as illustrated in the above examples, butalso in a fully continuous fashion, without departing from the scopethereof. Thus, a solution or suspension of an a,u-disubstituted,B-halopropionamide in a polar organic solvent not possessing a labilehydrogen atom may be introduced to a stirred, heated reaction vesselmaintained under a reduced pressure and surmounted by an outlet forremoving vapors. A solution of suspension or the alkoxide-typedehydrohalogenating agent is introduced into the vessel simultaneously,and at a rate substantially chemically equivalent to but not exceedingthat of the haloamide. The ,B-lactam product vaporizes as quickly as itis formed, along with a portion of the solvent. By-product alkali halideis removed from the liquid mixture contained in the vessel by a separatecontinuous filtration or centrifugation procedure, from which thefiltrate may be returned to the vessel directly or by addition to theliquid feed. The vapors from the vessel are led to one or morefractional distillation columnsin which the vapors are separated into 2or more components. The by-product tertiary alcohol is separatedthereby, and the fl-lactam is isolated in either a substantially purestate or as a solution in the polar solvent. The fi-lactam is thenconducted to polymerization equipment wherein it is converted to apolyamide. This polymerization is carried out in a polar solvent whichis either the same as that in which the ,B-lactam is prepared, or adifferentspecies of polar solvent as defined in this invention. Thepolymerization is carried out with a series of stirred vessels, thelactam, solvent, lactarn-polymerization catalyst, and (optionally) apromoter or molecular weight regulation all being added to the first vessel. The polymerizing mixture flows through the first vessel and thenthrough one or more additional polymerizing vessels connected seriallyto it. The mixture containing the polyamide is withdrawn from the lastvessel of the series and transferred to a polymer isolation step, fromwhich recovered polar solvent is recycled.

EXAMPLE XVI A 2-liter three neck flask was charged with a solution of180 g- (1.0 mole) bromopivalamide and then cooled to C. Sodium hydride,1 mole of a 50% suspension in mineral oil, was added portionwise at 0 C.and the mixture stirredat 0 C. for 1.5 hours after the addition, Thereaction mixture was then heated to 65 C. and maintained at thistemperature for one hour. The solution was filtered and stripped of mostof the dimethylacetamide, and then distilled. No fraction showed nitrileabsorption at 4.5;]. in the infrared, indicating that essentially nohydroxypivalonitrile was present.

EXAMPLE XVII In a container was charged 90 g. (0.50 mole) ofbromopivalamide and 1000 ml. dry benzene. Sodium hydride suspension(53.5% in mineral oil), 22.5 g., was added portionwise to the stirredmixture over a period of one hour, during which time the solution becameclear and then became a thick pasty mass. The temperature of thereaction mixture was maintained between 20 and 25 C. during theaddition. The mixture was then refluxed overnight. The benzene solution,isolated by filtration from precipitated solid, showed strong carbonylabsorption at 5 .7 characteristic of pivalolactam. An absorption at 4.5n indicated the presence of nitrile. The solution was stripped ofbenzene and the residue distilled at reduced pressure to give twofractions.

12 EXAMPLE XVIII Cut B.P., 0. (mm.) Reflux Wt, g. m,

Ratio 1 Total take OE.

All fractions showed strong carbonyl absorption in the infrared at5.7,u, characteristic of pivalolactam. Each fraction showed nitrileabsorption at 4.5a, the intensity of which increased quite markedly fromcut 1 to cut 3.

Fractions 2 and 3 were polymerized in hexamethylphosphoramide in thefollowing manner. Pivalolactam, 15 g., was mixed with ml. HMPA under drynitrogen in a 300-ml. round bottom flask previously dried by flamingunder a current of dry nitrogen. Initiator, comprising 0.030 g. sodiumhydride (53.5% in mineral oil) and one dip of acetic anhydride, was thenadded and the mixture swirled to homogenize and finally suspended in anoil bath maintained at 60 C. Additional sodium hydride was added after 3hours, and polymerization allowed to proceed for 19 hours.

Polymer was isolated by precipitation into water, and purificationefiected by Washing and drying. In this manner cut 2 gave 11.4 g. (76%)of polymer having ninh 0.64. No polymer separated on pouring out 3 intowater.

As can be seen from Examples XVI through XVIII, the use of a polarsolvent for the fl-lactam preparation surprisingly eliminates theproduction of the hydroxypivalonitrile impurity which unless removedfrom the lactam inhibits the production of high molecular weightpolypivalolactam.

EXAMPLE XIX A 3-liter three neck flask equipped with a motor drivenpaddle stirrer, heating mantle and reflux condenser topped with acalcium chloride tube was charged with 180 g. (2.0 moles) ofbromopivalamide dissolved in 750 ml. of dry tetrahydrofuran. Thesolution was then stirred without external heating while 45 gfof a 53.5%suspension of sodium hydride in mineral oil was added over a period often minutes. The reaction evolved gas and caused' gentle reflux whilethe sodium derivative of bromopivalamide separated as a fine whitesolid. The reaction mixture was refluxed 2 hours and the tetrahydrofuransolution of pivalolactam then separated by filtration from white solid.Solvent was removed by distillation at atmospheric pressure and theresidue then distilled at reduced pressure to give three fractions.

1 Yield, 26%.

No cut showed infrared absorption due to a nitrile grouping, which forhydroxypivalonitrile appears at 4.5a.

What is claimed is:

A coupled process for producing polyamides of the formula 13 wherein Rand R are .as defined below, which comprises reacting equimo-larproportions of a compound of the formula:

E i R wherein X is selected from the group consisting of Cl and Br; Rand R, which may be the same, are selected from the group ofchloromethyl, phenyl, alkyl and cyoloalkyl of up to six carbon atoms andmay together with C- to which they are attached form an a'licyclichydrooanbon ring of up to six carbon atoms, and a compound of theformula (R") M wherein M is selected from the class of alkali andalkaline earth metals; n is the valence of M; and R" is selected rfromthe group consisting of hydrogen, tertiary alkoxy, and hydrocarbon ofunder 20 carbon atoms, at a temperature of between about 70 and 120 C.

References Cited UNITED STATES PATENTS 2,500,317 3/1950 Lincoln 260-783,073,618 6/1963 Graf et a1 260-48 3,211,706 10/1965 Borner 260'-783,220,983 11/1965 Schmidt et a1 260-78 WILLIAM H. SHORT, PrimaryExaminer.

H. D. ANDERSON, Assistant Examiner.

